ctx

A context object that is passed to the implementation function for a rule or aspect. It provides access to the information and methods needed to analyze the current target.

In particular, it lets the implementation function access the current target's label, attributes, configuration, and the providers of its dependencies. It has methods for declaring output files and the actions that produce them.

Context objects essentially live for the duration of the call to the implementation function. It is not useful to access these objects outside of their associated function.See the Rules page for more information.

DEPRECATED. Use ctx.actions.run() or ctx.actions.run_shell(). Creates an action that runs an executable or a shell command. You must specify either command or executable.
Actions and genrules are very similar, but have different use cases. Actions are used inside rules, and genrules are used inside macros. Genrules also have make variable expansion.

aspect_ids

attr

A struct to access the values of the attributes. The values are provided by the user (if not, a default value is used). The attributes of the struct and the types of their values correspond to the keys and values of the attrs dict provided to the rule function. See example of use.

bin_dir

build_file_path

Returns path to the BUILD file for this rule, relative to the source root.

build_setting_value

unknown ctx.build_setting_value

Experimental. This API is experimental and may change at any time. Please do not depend on it. It may be enabled on an experimental basis by setting --experimental_build_setting_apiExperimental. This field is experimental and subject to change at any time. Do not depend on it.

Returns the value of the build setting that is represented by the current target. It is an error to access this field for rules that do not set the build_setting attribute in their rule definition.

configuration

coverage_instrumented

Returns whether code coverage instrumentation should be generated when performing compilation actions for this rule or, if target is provided, the rule specified by that Target. (If a non-rule or a Starlark rule Target is provided, this returns False.) Checks if the sources of the current rule (if no Target is provided) or the sources of Target should be instrumented based on the --instrumentation_filter and --instrument_test_targets config settings. This differs from coverage_enabled in theconfiguration, which notes whether coverage data collection is enabled for the entire run, but not whether a specific target should be instrumented.

Parameters

A Target specifying a rule. If not provided, defaults to the current rule.

created_actions

SkylarkValue ctx.created_actions()

For rules with _skylark_testable set to True, this returns an Actions provider representing all actions created so far for the current rule. For all other rules, returns None. Note that the provider is not updated when subsequent actions are created, so you will have to call this function again if you wish to inspect them.

This is intended to help write tests for rule-implementation helper functions, which may take in a ctx object and create actions on it.

executable

A struct containing executable files defined in label type attributes marked as executable=True. The struct fields correspond to the attribute names. Each value in the struct is either a file or None. If an optional attribute is not specified in the rule then the corresponding struct value is None. If a label type is not marked as executable=True, no corresponding struct field is generated. See example of use.

expand_location

Expands all $(location ...) templates in the given string by replacing $(location //x) with the path of the output file of target //x. Expansion only works for labels that point to direct dependencies of this rule or that are explicitly listed in the optional argument targets.

$(location ...) will cause an error if the referenced target has multiple outputs. In this case, please use $(locations ...) since it produces a space-separated list of output paths. It can be safely used for a single output file, too.

This function is useful to let the user specify a command in a BUILD file (like for genrule). In other cases, it is often better to manipulate labels directly.

expand_make_variables

Deprecated. Use ctx.var to access the variables instead.Returns a string after expanding all references to "Make variables". The variables must have the following format: $(VAR_NAME). Also, $$VAR_NAME expands to $VAR_NAME. Examples:

features

file

A struct containing files defined in label type attributes marked as allow_single_file. The struct fields correspond to the attribute names. The struct value is always a file or None. If an optional attribute is not specified in the rule then the corresponding struct value is None. If a label type is not marked as allow_single_file, no corresponding struct field is generated. It is a shortcut for:

new_file

new_file(filename): Creates a file object with the given filename in the current package.

new_file(file_root, filename): Creates a file object with the given filename under the given file root.

new_file(sibling_file, filename): Creates a file object in the same directory as the given sibling file.

new_file(file_root, sibling_file, suffix): Creates a file object with same base name of the sibling_file but with different given suffix, under the given file root.

Does not actually create a file on the file system, just declares that some action will do so. You must create an action that generates the file. If the file should be visible to other rules, declare a rule output instead when possible. Doing so enables Bazel to associate a label with the file that rules can refer to (allowing finer dependency control) instead of referencing the whole rule.

Parameters

outputs

A pseudo-struct containing all the predeclared output files, represented by File objects. See the Rules page for more information and examples.

This field does not exist on aspect contexts, since aspects do not have predeclared outputs.

The fields of this object are defined as follows. It is an error if two outputs produce the same field name or have the same label.

If the rule declares an outputs dict, then for every entry in the dict, there is a field whose name is the key and whose value is the corresponding File.

For every attribute of type attr.output that the rule declares, there is a field whose name is the attribute's name. If the target specified a label for that attribute, then the field value is the corresponding File; otherwise the field value is None.

For every attribute of type attr.output_list that the rule declares, there is a field whose name is the attribute's name. The field value is a list of File objects corresponding to the labels given for that attribute in the target, or an empty list if the attribute was not specified in the target.

(Deprecated) If the rule is marked executable or test, there is a field named "executable", which is the default executable. It is recommended that instead of using this, you pass another file (either predeclared or not) to the executable arg of DefaultInfo.

resolve_command

(Experimental) Returns a tuple (inputs, command, input_manifests) of the list of resolved inputs, the argv list for the resolved command, and the runfiles metadata required to run the command, all of them suitable for passing as the same-named arguments of the ctx.action method.

split_attr

A struct to access the values of attributes with split configurations. If the attribute is a label list, the value of split_attr is a dict of the keys of the split (as strings) to lists of the ConfiguredTargets in that branch of the split. If the attribute is a label, then the value of split_attr is a dict of the keys of the split (as strings) to single ConfiguredTargets. Attributes with split configurations still appear in the attr struct, but their values will be single lists with all the branches of the split merged together.